In wireless communications, CSI (channel state information) refers to known channel properties of a communication link. This information describes how a signal propagates from the transmitter to the receiver and represents the combined effect of, for example, scattering, fading, and power decay with distance. The CSI makes it possible to adapt transmissions to current channel conditions, which is crucial for achieving reliable communication with high data rates in multi-antenna systems.
CSI needs to be estimated at the receiver and usually quantized and feedback to the transmitter. Since the channel condition vary, instantaneous CSI needs to be estimated on a short-term basis. A popular approach is so-called training sequence (or pilot sequence), where a known signal is transmitted and a channel response matrix H is estimated using the combined knowledge of the transmitted and the received signal.
The accuracy of channel estimation is essential to receiver performance. For high modulations such as 256QAM and 1024QAM, enhancing channel estimation accuracy can significantly improve PER performance. For 1024QAM, enhancing channel estimation accuracy also helps reduce the TX and RX EVM requirement. Channel estimation inaccuracy is one key factor that degrades the performance of wireless networks. In wireless networks, various methods of enhancing channel estimation accuracy have been widely used. For example, channel smoothing when the channels of adjacent sub-carriers are similar, data-aided feedback channel tracking when complexity and latency are not critical, and pilots-based channel tracking when pilots are enough.
IEEE 802.11 is a set of standards for implementing wireless local area network (WLAN) communication in the 2.4, 3.6, 5, and 60 GHz frequency bands. Within the IEEE 802.11 standards, IEEE 802.11ac covers very high throughput with potential improvements over IEEE 802.11n, IEEE 802.11ah covers Sub 1 GHz sensor network and smart metering, and upcoming IEEE 802.11ax considers the improvement of spectrum efficiency to enhance the system throughput in high-density scenarios of wireless devices and will become a successor to IEEE 802.11ac. Beam-change indication can be used to significantly enhance channel estimation at receiver. In the present invention, a useful method of beam-change indication is proposed to enhance channel estimation performance based on the IEEE 802.11ax and the upcoming IEEE 802.1ah standards.